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How Is Precast Concrete Made(2)?

- Sep 21, 2018 -

Concrete and poured concrete

Precast concrete consists of coarse aggregates and fine aggregates, cement, water and admixtures. It is mixed in the factory's batch plant according to the engineer's specified concrete mix design.

Each infrastructure factory has a concrete laboratory for routine raw material testing and controlling the exact amount of each material in a given batch. This is especially important when using high flow self-consolidating concrete or SCC because concrete can flow quickly and easily, completely filling the mold and minimizing the possibility of cavitation.

The laboratory collects vials to check the compressive strength and verify the quality of each batch. The concrete was also subjected to various additional tests, including spreading tests, to verify that the mixture had proper fluidity and that there was no separation of the aggregate.

A batch of approved concrete is transported into the mold in a dispenser using an overhead crane. When the crane is positioned above the mold, the production team fills the required amount of concrete in each form, taking care to completely fill the mold without clogging the air gap. Many plants use shakers to ensure that concrete is completely deposited into the formwork. Once the table is filled, flatten the top and apply the specified surface treatment.

Cured concrete

Immediately after the concrete is poured, the curing process begins. This may include placing a tarp on the product overnight to capture the heat generated as part of the hydration process, which accelerates the cure. The controlled environment of the prefabricated plant enables the product to cure correctly and achieve full design strength faster than the field.

Strip the form and check the product

Once the quality control technician confirms that the product has reached the required strength (2500 - 3000 psi) to remove the concrete from its form, the stripping process can begin. This involves opening the outer jacket of the mold and folding the inner core, attaching the hook of the crane to the lifting hardware, and moving the product through the crate to the inspection and finishing area after pouring.

There, QC technicians review the structure to ensure that the final product matches the production drawings and there are no visual defects. Once the final quality control check is passed and the technician signs it, the product is tagged and shipped to the yard, waiting to be delivered to the project site.

Pre-confirm at your workplace

Will the prefabricated parts be delivered to your job site? Using prefabrication saves time and money while improving the overall quality of the construction, but how do you know if prefabrication is right for your project? With all the variables and options, figuring out can be tricky. Download Precast Benefits Checklist and you will be able to quickly assess when, where and how prefabrication is used in your project.